Give it one more try. Don't "converse," just ask for a date and time to meet and complete the transaction. If you get any more beating around of shrubbery, just ask straight out: "Look, do you want to sell the gun or not? I answered a For Sale ad and I'm ready to buy. If you don't want to sell it, say so and I'll look elsewhere."
There's no way you're the bad guy if a seller is jerking your chain. He may perceive you that way but, if so, that's his problem.